Name: proposal-modules-pragma
Owner: Ecma TC39
Description: Proposal to recognize a `"use module";` pragma
Created: 2017-05-15 21:31:15.0
Updated: 2018-04-21 12:10:34.0
Pushed: 2017-05-29 08:42:15.0
Homepage: https://tc39.github.io/proposal-modules-pragma/
Size: 21
Language: HTML
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"use module";This proposal is in stage 1 of the TC39 process.
Since the Script and Module syntaxes have some overlap (in particular, most modules with no import or export declarations are valid scripts), there are situations where either a host environment or simply a human reader may not be able to infer whether a piece of code is intended to be a script vs a module.
Some host environments may offer out-of-band mechanisms for specifying the mode, such as HTML attributes (<script type=module>), configuration parameters ("module": "main.js"), command-line switches (node -m), or file extensions (.mjs). However, an in-band pragma for enforcing the mode can be useful for a number of reasons:
Finally, the fact that this is a pragma means that ecosystems where there is no formal or conceptual ambiguity – in particular, ecosystems that author entirely using modules – do not need to pollute their source code.
Today, programmers can use a programming pattern to enforce that a file is a module:
rt {};
This syntax has no effect except to force a parsing error if a host environment attempts to parse it as a script.
This is suboptimal for readability, since it does not clearly convey what its intended effect is. And it's also not applicable to the problem of enforcing that a source file is intended to be parsed as a script.